Question

Ok i got this markup

<th class="ai1ec-weekday <?php if( $day['today'] ) echo 'ai1ec-today' ?>">
    <span class="ai1ec-weekday-date"><?php
    echo Ai1ec_Time_Utility::date_i18n( 'l', $date, true );
    ?> </span>
</th>

which produces this output as the span has text-align: center

now i want to add a button which is floated to the right

<th class="ai1ec-weekday <?php if( $day['today'] ) echo 'ai1ec-today' ?>">
    <div class="btn-group pull-right">
        <button class="btn ai1ec-reveal-events"><?php _e( 'Reveal all events', AI1EC_PLUGIN_NAME ) ?></button> 
    </div>
    <span class="ai1ec-weekday-date"><?php
    echo Ai1ec_Time_Utility::date_i18n( 'l', $date, true );
    ?> </span>
</th>

and this is what i get

what i would like to obtain is that mondais still centered as it was before, but i would like to do that without using absolute positioning (if it’s possible, of course)

the CSS ( i mean other than bootstrap CSS )

.ai1ec-week-view th .ai1ec-weekday-date,
.ai1ec-oneday-view th .ai1ec-weekday-date {
  font-size: 10.5pt !important;
  font-weight: normal !important;
}
.ai1ec-week-view th .ai1ec-weekday-day {
  font-size: 9pt !important;
  font-weight: normal !important;
}
.ai1ec-month-view th, .ai1ec-oneday-view th {
    text-align: center !important;
}

Answer 1

see this approach: http://jsbin.com/uxejes/1/edit
(tested only on Fx18 and Chrome)

relevant css

button {
  float: right; 
  margin-right: -100%;
  position: relative;
  left: -100%;
}

span {
  display: block;
  text-align: center;
}

the button (with position: relative) won’t affect the position of the text contained inside the span element