Alright so I just set-up a test forum real quick and tried a couple of different methods for changing the Start New Topic and Locked buttons. This, so far is what has worked best for me. Keep in mind that it is not the best, nor is it the only way of accomplishing what you are asking for.
In ipb_style.css find (Do not include the "{...}" in your search)
For the Start New Topic button
.topic_buttons li.important a, .topic_buttons li.important span, .ipsButton .important,
.topic_buttons li a, .topic_buttons li span, .ipsButton {...}
Under this add
.topic_buttons li.startNewTopic a{
padding: 20px 20px 20px 20px;
}
For the Locked button, either search for topic_button_closed.png or find (Do not include the "{...}" in your search)
.topic_buttons li.important a, .topic_buttons li.important span, .ipsButton .important, .ipsButton.important{...}
Under This add
.topic_buttons li.lockedTopic a{
padding: 20px 20px 20px 20px;
}
Now for the Start New Topic button open forumIndexTemplate under Forum View and search for the following bit of code
accesskey='s'
There will be two different bits of code containing this accesskey, one each for the top and bottom Start New Topic buttons. Both of them should look similar to these
Top
<ul class='topic_buttons'>
<if test="usercanpost:|:$forum_data['_user_can_post']">
<li><a href='{parse url="module=post&section=post&do=new_post&f={$forum_data['id']}" base="publicWithApp"}' title='{$this->lang->words['topic_start']}' accesskey='s'>{$this->lang->words['topic_start']}</a></li>
<else />
Bottom
<ul class='topic_buttons'>
<if test="bottomusercanpost:|:$forum_data['_user_can_post']">
<li><a href='{parse url="module=post&section=post&do=new_post&f={$forum_data['id']}" base="publicWithApp"}' title='{$this->lang->words['topic_start']}' rel='nofollow' accesskey='s'{$this->lang->words['topic_start']}</a></li>
<else />
Now all you have to do is tweak both of these just a little bit so they look like so
<ul class='topic_buttons'>
<if test="usercanpost:|:$forum_data['_user_can_post']">
<li class='startNewTopic'><a href='{parse url="module=post&section=post&do=new_post&f={$forum_data['id']}" base="publicWithApp"}' title='{$this->lang->words['topic_start']}' accesskey='s'>{$this->lang->words['topic_start']}</a></li>
<else />
and
<ul class='topic_buttons'>
<if test="bottomusercanpost:|:$forum_data['_user_can_post']">
<li class='startNewTopic'><a href='{parse url="module=post&section=post&do=new_post&f={$forum_data['id']}" base="publicWithApp"}' title='{$this->lang->words['topic_start']}' rel='nofollow' accesskey='s'>{$this->lang->words['topic_start']}</a></li>
<else />
Now back to the Locked button, open topicViewTemplate under Forum View and search for the following bit of code
accesskey='r'
There will be three different bits of code containing this accesskey, we just want the first one.
<ul class='topic_buttons'>
<if test="closedButton:|:$displayData['reply_button']['image'] == 'locked'">
<li class='important'>
<if test="pollOnly:|:isset($displayData['poll_data']['poll']['poll_only']) && $displayData['poll_data']['poll']['poll_only']">
<if test="closedButtonLink:|:$displayData['reply_button']['url']">
<a href='{$displayData['reply_button']['url']}' accesskey='r'>{parse replacement="lock_icon"} {$this->lang->words['top_poll_only_reply']}</a>
<else />
Just edit the top bit to include our 'lockedTopic' subClass
<ul class='topic_buttons'>
<if test="closedButton:|:$displayData['reply_button']['image'] == 'locked'">
<li class='important lockedTopic'>
<if test="pollOnly:|:isset($displayData['poll_data']['poll']['poll_only']) && $displayData['poll_data']['poll']['poll_only']">
<if test="closedButtonLink:|:$displayData['reply_button']['url']">
<a href='{$displayData['reply_button']['url']}' accesskey='r'>{parse replacement="lock_icon"} {$this->lang->words['top_poll_only_reply']}</a>
<else />
Here is a quick before and after of the Start New Topic button
and Locked button
You can make a separate subClass for each button you wanted to change, so that way you can change each one to your liking, or you can just make one general one for them. In my example I made one specifically for the Start New Topic and Locked buttons.