Actually, you should be able to accomplish that with pure CSS. Try the following.
- For Blog Post display pages:
.ms-PostWrapper, .ms-commentsWrapper, .ms-CommentFooter {width: 100%;}
td.ms-bodyareaframe table#MSO_ContentTable tbody tr td table,
#part1 .ms-formtable .ms-formbody,
#part1 .ms-formtable ms-formbody span,
#part1 .ms-formtable .ms-formbody .ms-long {width: 100% !important;}
#part1 .ms-formtable .ms-formlabel {width: 12% !important;}
- For Blog Post edit pages:
td.ms-formareaframe table.ms-propertysheet table.ms-propertysheet,
table#onetIDListForm,
table#onetIDListForm .ms-formbody span table.ms-long,
table#onetIDListForm .ms-formbody span span table.ms-long,
table#onetIDListForm .ms-formbody input.ms-long,
table#onetIDListForm .ms-formbody textarea.ms-long,
table#onetIDListForm .ms-formbody table.ms-long,
table#onetIDListForm .ms-usereditor,
table#onetIDListForm .ms-RadioText
{
width: 100% !important;
}
table#onetIDListForm .ms-formbody span span div iframe,
table#onetIDListForm iframe.ms-rtelong
{
width: 100%;
}
table#onetIDListForm .ms-formbody,
table#onetIDListForm #formTbl .ms-formbody span input.ms-input
{
width: 99.1%;
}
td.ms-formbody table.ms-rtetoolbarmenu
{
width: ;
}
td.ms-dtinput input.ms-input
{
width: 136px !important;
}
span#partAttachment td#attachmentsOnClient,
span#partAttachment td#attachmentsOnClient span input.ms-fileinput
{
width: 90% !important;
}
table#onetIDListForm .ms-inputuserfield
{
width: auto !important;
}
table#onetIDListForm .ms-formbody span table.ms-long td.ms-input
{
width: 33%;
}
table#onetIDListForm .ms-formbody span table.ms-long td.ms-input div
{
border: 1px solid #b2b2b2 !important;
overflow-x: hidden !important;
width: 100% !important;
*width: 99% !important;
}
table#onetIDListForm .ms-formbody span table.ms-long td.ms-input div select
{
border: none !important;
width: 109% !important;
*width: 102% !important;
*margin-left: -3px !important;
*margin-top: -3px !important;
}
EDIT: I tried to pretty format the CSS code but unfortunately couldn't get it working. Sorry!
